powershell containers on docker hub can't be referenced by powershell version

[pessimism]

Steps to reproduce the issue:

1. docker pull microsoft/powershell:centos7
2. observe powershell version in startup marquee
3. docker pull microsoft/powershell:centos7 again a few weeks later
4. observe powershell version in startup marquee

What actually happened?:
build of powershell inside this container image changed as if it were a LATEST tagged container

What did you expect to happen?:
container should be tagged with a version, such as microsoft/powershell:centos7-6.0.0-rc2

Additional information:
This applies to several of the other linux flavored powershell containers. the nanoserver ones do append a powershell version to the docker tag already.